Welcome to the Evans Group Website. Our objective is to provide useful information to the chemical community that is relevant to our research and teaching activities. It is our hope that prospective graduate students and postdoctoral collaborators might be introduced to the types of research projects that are being pursued in our laboratory from the "Research" and "Publications" sections. The "Current Members" section should give an accurate perspective of both group size and diversity. If you want to find out where the graduates go after their appointments in the group, go to the "Former Members" database and identify those individuals who have pursued either academic or industrial careers. Throughout the academic year, group members participate in an informal seminar series where literature topics relevant to our research interests are presented. If you go to the "Group Seminars" data base you will find a list of the topics covered. A downloadable PDF file of many of the individual presentations is also available. We have also provided a searchable archive of selected past seminars that the community might find useful. Present and former group members have found these literature reviews invaluable; accordingly, we now offer them to you as well.

Teicoplanin (1), isolated in 1978 from Actinoplanes teichomyceticus, is a member of a large family of glycopeptide antibiotics which includes vancomycin. Teicoplanin and vancomycin are the only two representatives of this family that are used clinically for the treatment of methicillin-resistant Staphylococcus aureus infections and are considered to be the antibiotics of last resort against this pathogen. The emergence of bacterial strains resistant to treatment by these glycopeptides, and the challenging structural features of these natural products, have prompted extensive investigations into the total syntheses of both vancomycin and teicoplanin (1). In this Communication, we report the total synthesis of teicoplanin aglycon (2) from the peptidic subunits I and II.

In this communication we outline a general strategy for the synthesis of the closely related natural products FR182877 (1) and hexacyclinic acid (2) from a common macrocyclic precursor via a sequence of transannular [4+2] cycloadditions. This approach has been validated by its successful application to the enantioselective synthesis of (—)-FR182877 providing confirmation of its assigned absolute configuration.

Callipeltoside A (1) was isolated from the lithistid sponge Callipelta sp. by Minale and co-workers in 1996. Preliminary biological assays indicated that this marine natural product exhibits cytotoxic activity against NSCLC-N6 human bronchopulmonary non-small-cell lung carcinoma and P388 cell lines.1 At the time this project was undertaken, the relative stereochemical relationships between the sugar and the macrolactone had been proposed on the basis of 2D-NMR studies. However, the relative stereochemistry of the chlorocyclopropyl side chain to the rest of the molecule and the absolute stereochemistry of callipeltoside A remained unassigned. In this Communication, we report a convergent synthesis of callipeltoside A from the illustrated subunits.

The first members of the pectenotoxin family of marine natural products were isolated off the northeastern coast of Japan in 1985. Subsequently, ten members of this group have been identified. The structural diversity within the pectenotoxins stems from variations in the C43 oxidation state, as well as the differing configurations of the AB spiroketal portion of the structures. Pectenotoxin-2 (C43 = Me) is cytotoxic towards human lung, colon and breast cancer cell lines with LC50 values in the nanomolar range. Pectenotoxins-1, -4, and –8 (C43 = CH2OH) are differentiated by their AB spiroketal subunits that are interconvertable by acid equilibration. In these two communications, we describe our efforts culminating in the synthesis of pectenotoxins-4 and -8.

Chiral aluminum complex 1 has been employed as a catalyst for the stereoselective synthesis of cis-2-oxazoline-4-carboxylates from the aldol reaction of the illustrated oxazole and aldehydes has been reported. The cis product diastereoselection ranges from 3-50:1 while enantioselectivities vary from 92-99%.

Publications 267 and 281 document the enantioselective glyoxylate addition reactions of allenylsilanes and silylketene acetals. The chiral scandium-pybox complexes are highly effective catalysts for these processes. Important counterion effects have beeen documented and an X-ray structure of the pentagonyl bipyramidyl 1(H2O) hydrate has been obtained (see below).

X-ray Crystal structures of Scandium Triflate–pybox Structures

Our group has been attempting to document the preferred coordination geometries and coordinacies of Sc(III)-pybox complexes. Several X-ray structures determined by us are provided. Pentagonal bipyramidal complexes may well form the basis of constructing catalyst substrate complexes.

Chiral auxilliary based direct aldol reactions are reported in publications 274 and 277. The reactions are catalytic in magnesium salts and are facilitated by silylation with chlorotrimethylsilane. The adducts isolated are in high diastereoselectivity (up to 32:1 dr) and favor the anti-aldol diastereomer. Reactions are operationally simple and can be run under ambient atmosphere without rigorous exclusion of water. a stereochemical rationale for both the anti diastereoselection and enolate face selelctivity is provided in publication 277.